Two members of the matrix metalloproteinase family which can cleave native types I, II and III triple helical collagens are collagenases from fibroblasts and neutrophils. These enzymes are the ...products of different genes which share structural motifs but are only 57% identical. In this study, we determined the site of cleavage in the alpha 1(I) chains and showed that the neutrophil collagenase acted at the same site as the fibroblast collagenase. We also used collagens as substrates which were generated by site-directed mutagenesis of the murine Col1a1 gene and found that the pattern of susceptibility to cleavage by purified neutrophil collagenase was indistinguishable from that previously described for the fibroblast collagenase. Collagens containing substitutions of Pro for Ile-776 (P1) were not cleaved; whereas those containing substitutions of Met for Ile-776 were cleaved. Type I collagen which contained alpha 1(I) chains in which there were double substitutions of Pro for Gln-774 (P2) and Ala-777 (P2') were also not cleaved. These type I collagens contained wild type alpha 2(I) chains as well as mutant alpha 1(I) chains in the mixed helical trimers; the alpha 2(I) chain in the trimers containing the resistant alpha 1(I) chains were also not cleaved by the neutrophil collagenase.
In a recent paper, the oscillator performance of GaAs Schottky-Read diodes of the type metal - n 1 n 2 n + was given (4). Efficiencies as high as 26% were observed at X-band for a ratio n 1 /n 2 ≈ ...25. The tuning characteristics of these diodes differ considerably from conventional IMPATTS which have uniform doping profiles. In addition, the Schottky-Read diodes have proved to be difficult to use in microstrip amplifier circuits, particularly at high rf input levels. Small and large signal admittance measurements were made at frequencies from 4 to 12 GHz for different dc current levels on a number of diodes with differing profiles, I-V characteristics, and oscillator performance. The results were compared with those obtained for conventional IMPATTS. In addition, the effect of structural variations on breakdown voltage and depletion depth were calculated.
